Good evening, I'm trying to find the cap for this pen

golden platignum.JPG

The cap I have is in these dreadful conditions

cap1.JPG
cap2.JPG

The pen writes nicely. Can somenoe point me in the correct direction to find it ? the 'bay' doesn't have anything similar to what I need. Is it worthwhile fixing it ? I got it for little money, still it would be nice to have it complete :-)

Thank you
Marco